I have plotted a 3D graph consisting of several 2D lines (z as function of x) for different values of y. It works well (although there is probably a much easier way), but the starting points of the different lines in the graph are not the same, i.e. they don't all start at x=0, what is the left boundary of my selected plotting range. It looks like, that every line starts exactly at the first data point that lies within the plotting range but not necessarily at x=0. This problem does not occur, when I plot any single line as a 2D graph within the same plotting range. Does anybody have any idea how to solve this?